Plaster moulded mantels, and columns provide a decorative enhancement to a fireplace opening. They are often formed from a mixture of gypsum plaster, for example beta hemihydrate, and gypsum cement such as alpha hemihydrate, which is approximately 4 times stronger than beta hemihydrate. Because gypsum forms easily, sets and gains strength quickly, it is an ideal material for manufacturing architectural and decorative structures. Advantageously, a casted piece can be removed from a mould within two to three hours after casting. Thus, it is a very accepted and used material, which can save time, space, and allow a mould to be reused shortly after pouring which is important in the overall process of mould formation.
Notwithstanding, there is a disadvantage to the aforementioned mixture. It is not ideal when used in high-heat applications, for example, when used as a fireplace surround in situ. Calcination of the material can occur in the presence of high heat, and the cast structure can lose the strength, crack and/or discolour.
It is an object of this invention to provide a composition with similar workability as the standard available gypsum cement commercial mixture and create a desired finish that is similar to a casted gypsum cement, referred to sometimes as a honed finish which is highly desirable, which can withstand high heat, discoloration and cracking while maintaining suitable strength when exposed to typical temperatures of a fireplace surround in indoor applications.
Commercially available glass fibre reinforced cement (GFRC) is sometimes used for this purpose, however it is not ideal. GFRCs are made from cement 20-30%+sand 70-80%+Glass fibre 3-5% (all by weight). Although GRFC withstands heat, it is not a preferred material because of its poor product-ability, pieces need minimum 24 hours to de-mould, its poor workability; it takes about 36 hours to be polish-able after casting, and it does not provide a desired honed look or feel.
To be a commercially viable and desirable product, texture is very important and when plain gypsum cement is sanded and polished, it becomes too smooth, shiny and marble like instead of having a duller honed look and feel. Therefore GFRC is not considered a preferred material.